Effect of SO₂ Impurities on Cu-Based Catalysts Prepared by Thermal Evaporation and Magnetron Sputtering for Electrochemical CO₂ Reduction

Introduction:Electrochemical CO₂ reduction reaction (CO₂RR) is a promising route for converting carbon dioxide into value-added products. Copper-based catalysts are particularly important materials for CO₂RR due to their ability to promote C-C coupling and produce multi-carbon products such as ethylen. Real CO₂ feed streams may contain impurities, including SO₂, which can affect catalytic activity, selectivity and long-term stability. Understanding how SO₂ interacts with different Cu surfaces is therefore essential for designing catalysts resistant to poisoning.

Methods:Cu-based catalytic layers were prepared by thermal evaporation and magnetron sputtering. Layers thickness were determined to compare the structural parameters resulting from both sputtering techniques. Their performance was evaluated during CO₂RR under a CO₂ stream containing 100 ppm SO₂. Product distribution and Faradaic efficiency was monitored during electrolysis with particular focus on ethylene formation. The catalysts were characterized before and after testing using XRD, SEM, AFM, ATR-FTIR, XPS and XRF. Post-reaction analysis was used to identify sulfur-containing species formed after SO₂ exposure.

Results:All investigated Cu-based catalysts showed comparable activity levels, with maximum FE toward C₂H₄ reaching approximately 25-40%. Although SEM revealed cracks after electrolysis, XPS did not detect sulfur species on the outer Cu surface, while XRF confirmed sulfur accumulation within the electrode structure. This suggests that sulfur-containing species accumulated mainly at the GDE/Cu interface rather than penetrating through the Cu layer to the exposed catalyst surface.

Conclusions:The obtained results will provide insight into the relationship between Cu preparation method, surface structure and susceptibility to SO₂ induced deactivation. This knowledge may support the development of Cu-based catalysts with improved stability for CO₂ conversion using impurity containing feed streams.